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Tomo Kitahashi

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Papers by Tomo Kitahashi

Research paper thumbnail of Deep-sea meiofauna off the Pacific coast of Tohoku and other trench slopes around Japan: a comparative study before and after the 2011 off the Pacific coast of Tohoku Earthquake

Journal of Oceanography, 2015

Research paper thumbnail of Sedimentary features of Onagawa Bay, northeastern Japan after the 2011 off the Pacific coast of Tohoku Earthquake: sediment mixing by recolonized benthic animals decreases the preservation potential of tsunami deposits

Journal of Oceanography, 2015

Research paper thumbnail of 熱水噴出域のメイオファウナの定量的研究におけるサンプラーバイアスについて：内径の異なる２種類のハンドコアラーによる堆積物の比較

JAMSTEC Report of Research and Development, 2010

Research paper thumbnail of Effects of mass sedimentation events after the 2011 off the Pacific coast of Tohoku Earthquake on benthic prokaryotes and meiofauna inhabiting the upper bathyal sediments

Journal of Oceanography, 2015

ABSTRACT We examined the effects of mass sedimentation events caused by the 2011 off the Pacific ... more ABSTRACT We examined the effects of mass sedimentation events caused by the 2011 off the Pacific coast of Tohoku Earthquake on abundances and vertical distributions of prokaryotes and metazoan meiofauna in sediments, using sediment cores collected from eight bathyal stations off Tohoku 1 year after the M9.0 earthquake. Event deposits 1–7 cm thick were observed at the topmost part of the sediment cores at all sampling stations. At some stations, prokaryotic cell abundances were lower in the surface event-deposit layers compared to those in deeper sediments. These variations were explained by environmental parameters such as a dimensionless sorting factor and mean grain size, suggesting that turbidite sedimentation affected prokaryotic cell abundances. Nematodes had anomalously higher subsurface abundances at the stations where subsurface peak prokaryotic cell numbers were observed, whereas copepods always showed peak densities in the sediment surface layer. Although there are no available data for prokaryotic cell abundances and meiofaunal densities before the earthquake from the same sites, it is likely that the subsurface peaks in prokaryotic cell numbers and nematode densities resulted from the sedimentation events. The effects of sedimentation events on the organisms were observed 1 year after the earthquake, indicating that episodic sedimentation events on scales of several centimeters have a large effect on small organisms inhabiting sediments.

Research paper thumbnail of Sampler Bias in the Quantitative Study on Meiofauna around Hydrothermal Vents: Comparisons of Sediments Collected Using Two Types of Handcorers with Different Diameters

Research paper thumbnail of Nematode community composition in hydrothermal vent and adjacent non-vent fields around Myojin Knoll, a seamount on the Izu-Ogasawara Arc in the western North Pacific Ocean

Research paper thumbnail of No genetic deviation between two morphotypes of the snipefishes (Macroramphosidae: Macroramphosus) in Japanese waters

Ichthyological Research, 2014

Research paper thumbnail of Effect of the 2011 Tohoku Earthquake on deep-sea meiofaunal assemblages inhabiting the landward slope of the Japan Trench

Marine Geology, 2014

ABSTRACT Meiofaunal assemblages inhabiting the landward slope of the Japan Trench (water depth, 1... more ABSTRACT Meiofaunal assemblages inhabiting the landward slope of the Japan Trench (water depth, 120–5,600 m) were examined 4.5 months and 1.5 years after the 2011 Tohoku Earthquake off Sanriku, Miyagi Prefecture, northeast Japan. Two key parameters were compared before (24–30 years) and after (4.5 months in 2011 and 1.5 years in 2012) the earthquake: (a) the bathymetric pattern and (b) the vertical distribution of meiofauna in the sediments. Differences in meiofaunal densities and associated bathymetric patterns were not detected before and after the earthquake. However, the vertical profiles of meiofauna in the sediments differed at some stations, with this observed change being maintained in both 2011 and 2012. Furthermore, the highest meiofaunal densities occurred in the subsurface layers in 2011 at some stations, with these subsurface peaks being no longer present in 2012. At these stations, the assemblage structure at the higher taxon level differed between 2011 and 2012, with copepod density increasing in 2012. Therefore, copepod abundance appeared to decrease because of the effect of earthquake-related events (e.g. rapid sedimentation induced by the turbidity current). These changes in meiofaunal vertical profiles and assemblage structures detected after the earthquake were probably caused by an increase in organic matter content in the topmost layers. These results indicate that major disturbances to deep-sea sediments mainly influenced the vertical distribution and assemblage structure of meiofauna after the 2011 Tohoku Earthquake, whereas meiofaunal densities remained similar or quickly recovered within 4.5 months of the event.

Research paper thumbnail of Bathymetric patterns of α and β diversity of harpacticoid copepods at the genus level around the Ryukyu Trench, and turnover diversity between trenches around Japan

Progress in Oceanography, 2014

Research paper thumbnail of Assemblages gradually change from bathyal to hadal depth: A case study on harpacticoid copepods around the Kuril Trench (north-west Pacific Ocean)

Deep-sea Research Part I-oceanographic Research Papers, 2013

Research paper thumbnail of Assemblages of Harpacticoida (Crustacea: Copepoda) from the Ryukyu and Kuril Trenches, north-west Pacific Ocean

Journal of the Marine Biological Association of the United Kingdom, 2012

Research paper thumbnail of Bathymetric patterns of meiofaunal abundance and biomass associated with the Kuril and Ryukyu trenches, western North Pacific Ocean

Deep-sea Research Part I-oceanographic Research Papers, 2011

The abundance and biomass of metazoan meiofauna and their relationships with environmental factor... more The abundance and biomass of metazoan meiofauna and their relationships with environmental factors [chloroplastic pigment equivalents (CPE) and sediment characteristics] were studied quantitatively around and within the Kuril Trench (560–7090 m) and the Ryukyu Trench (1290–7150 m), which are located in eutrophic and oligotrophic regions, respectively, of the western North Pacific. Faunal abundance and biomass, as well as the CPE content of sediments, were considerably higher in the Kuril region than in the Ryukyu region. In both cases, CPE tended to decrease with water depth, but relatively high values were found in the deepest areas, suggesting that organic matter has accumulated in both trenches. Meiofaunal abundance and biomass were lower than expected from sediment CPE values at hadal stations below 6000 m. Differences in the density and biomass of meiofauna between these two trenches appeared to reflect differences in overall ocean productivity above them. When the analysis was restricted to each region, however, no association was found between the abundance and biomass of meiofauna and food availability. Furthermore, the factors regulating the bathymetric patterns in these meiofaunal parameters appeared to differ between the two trenches.► The abundance and biomass of metazoan meiofauna and their relationships with environmental factors were studied around the Kuril Trench and the Ryukyu Trench. ► Organic matter suggested to be accumulated in both trenches. ► No association was found between the abundance and biomass of meiofauna and food availability in any trench. ► The factors regulating the bathymetric patterns in these meiofaunal parameters appeared to differ between the two trenches.

Research paper thumbnail of Deep-sea meiofauna off the Pacific coast of Tohoku and other trench slopes around Japan: a comparative study before and after the 2011 off the Pacific coast of Tohoku Earthquake

Journal of Oceanography, 2015

Research paper thumbnail of Sedimentary features of Onagawa Bay, northeastern Japan after the 2011 off the Pacific coast of Tohoku Earthquake: sediment mixing by recolonized benthic animals decreases the preservation potential of tsunami deposits

Journal of Oceanography, 2015

Research paper thumbnail of 熱水噴出域のメイオファウナの定量的研究におけるサンプラーバイアスについて：内径の異なる２種類のハンドコアラーによる堆積物の比較

JAMSTEC Report of Research and Development, 2010

Research paper thumbnail of Effects of mass sedimentation events after the 2011 off the Pacific coast of Tohoku Earthquake on benthic prokaryotes and meiofauna inhabiting the upper bathyal sediments

Journal of Oceanography, 2015

ABSTRACT We examined the effects of mass sedimentation events caused by the 2011 off the Pacific ... more ABSTRACT We examined the effects of mass sedimentation events caused by the 2011 off the Pacific coast of Tohoku Earthquake on abundances and vertical distributions of prokaryotes and metazoan meiofauna in sediments, using sediment cores collected from eight bathyal stations off Tohoku 1 year after the M9.0 earthquake. Event deposits 1–7 cm thick were observed at the topmost part of the sediment cores at all sampling stations. At some stations, prokaryotic cell abundances were lower in the surface event-deposit layers compared to those in deeper sediments. These variations were explained by environmental parameters such as a dimensionless sorting factor and mean grain size, suggesting that turbidite sedimentation affected prokaryotic cell abundances. Nematodes had anomalously higher subsurface abundances at the stations where subsurface peak prokaryotic cell numbers were observed, whereas copepods always showed peak densities in the sediment surface layer. Although there are no available data for prokaryotic cell abundances and meiofaunal densities before the earthquake from the same sites, it is likely that the subsurface peaks in prokaryotic cell numbers and nematode densities resulted from the sedimentation events. The effects of sedimentation events on the organisms were observed 1 year after the earthquake, indicating that episodic sedimentation events on scales of several centimeters have a large effect on small organisms inhabiting sediments.

Research paper thumbnail of Sampler Bias in the Quantitative Study on Meiofauna around Hydrothermal Vents: Comparisons of Sediments Collected Using Two Types of Handcorers with Different Diameters

Research paper thumbnail of Nematode community composition in hydrothermal vent and adjacent non-vent fields around Myojin Knoll, a seamount on the Izu-Ogasawara Arc in the western North Pacific Ocean

Research paper thumbnail of No genetic deviation between two morphotypes of the snipefishes (Macroramphosidae: Macroramphosus) in Japanese waters

Ichthyological Research, 2014

Research paper thumbnail of Effect of the 2011 Tohoku Earthquake on deep-sea meiofaunal assemblages inhabiting the landward slope of the Japan Trench

Marine Geology, 2014

ABSTRACT Meiofaunal assemblages inhabiting the landward slope of the Japan Trench (water depth, 1... more ABSTRACT Meiofaunal assemblages inhabiting the landward slope of the Japan Trench (water depth, 120–5,600 m) were examined 4.5 months and 1.5 years after the 2011 Tohoku Earthquake off Sanriku, Miyagi Prefecture, northeast Japan. Two key parameters were compared before (24–30 years) and after (4.5 months in 2011 and 1.5 years in 2012) the earthquake: (a) the bathymetric pattern and (b) the vertical distribution of meiofauna in the sediments. Differences in meiofaunal densities and associated bathymetric patterns were not detected before and after the earthquake. However, the vertical profiles of meiofauna in the sediments differed at some stations, with this observed change being maintained in both 2011 and 2012. Furthermore, the highest meiofaunal densities occurred in the subsurface layers in 2011 at some stations, with these subsurface peaks being no longer present in 2012. At these stations, the assemblage structure at the higher taxon level differed between 2011 and 2012, with copepod density increasing in 2012. Therefore, copepod abundance appeared to decrease because of the effect of earthquake-related events (e.g. rapid sedimentation induced by the turbidity current). These changes in meiofaunal vertical profiles and assemblage structures detected after the earthquake were probably caused by an increase in organic matter content in the topmost layers. These results indicate that major disturbances to deep-sea sediments mainly influenced the vertical distribution and assemblage structure of meiofauna after the 2011 Tohoku Earthquake, whereas meiofaunal densities remained similar or quickly recovered within 4.5 months of the event.

Research paper thumbnail of Bathymetric patterns of α and β diversity of harpacticoid copepods at the genus level around the Ryukyu Trench, and turnover diversity between trenches around Japan

Progress in Oceanography, 2014

Research paper thumbnail of Assemblages gradually change from bathyal to hadal depth: A case study on harpacticoid copepods around the Kuril Trench (north-west Pacific Ocean)

Deep-sea Research Part I-oceanographic Research Papers, 2013

Research paper thumbnail of Assemblages of Harpacticoida (Crustacea: Copepoda) from the Ryukyu and Kuril Trenches, north-west Pacific Ocean

Journal of the Marine Biological Association of the United Kingdom, 2012

Research paper thumbnail of Bathymetric patterns of meiofaunal abundance and biomass associated with the Kuril and Ryukyu trenches, western North Pacific Ocean

Deep-sea Research Part I-oceanographic Research Papers, 2011

The abundance and biomass of metazoan meiofauna and their relationships with environmental factor... more The abundance and biomass of metazoan meiofauna and their relationships with environmental factors [chloroplastic pigment equivalents (CPE) and sediment characteristics] were studied quantitatively around and within the Kuril Trench (560–7090 m) and the Ryukyu Trench (1290–7150 m), which are located in eutrophic and oligotrophic regions, respectively, of the western North Pacific. Faunal abundance and biomass, as well as the CPE content of sediments, were considerably higher in the Kuril region than in the Ryukyu region. In both cases, CPE tended to decrease with water depth, but relatively high values were found in the deepest areas, suggesting that organic matter has accumulated in both trenches. Meiofaunal abundance and biomass were lower than expected from sediment CPE values at hadal stations below 6000 m. Differences in the density and biomass of meiofauna between these two trenches appeared to reflect differences in overall ocean productivity above them. When the analysis was restricted to each region, however, no association was found between the abundance and biomass of meiofauna and food availability. Furthermore, the factors regulating the bathymetric patterns in these meiofaunal parameters appeared to differ between the two trenches.► The abundance and biomass of metazoan meiofauna and their relationships with environmental factors were studied around the Kuril Trench and the Ryukyu Trench. ► Organic matter suggested to be accumulated in both trenches. ► No association was found between the abundance and biomass of meiofauna and food availability in any trench. ► The factors regulating the bathymetric patterns in these meiofaunal parameters appeared to differ between the two trenches.

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